11/27/05 FCST: Southern Plains

[nickgrillo]

Making it short for now... A synoptic trough will continue to amplify as it pushes into the Mississippi Valley on MON with rich boundary layer moisture forecasted to advect northward in response to a 40kt SW LLJ spread across the warm sector... This will result a favorable setup for severe thunderstorms, including the potential for AT LEAST a widespread damaging wind event. Overall, the threat should extend from eastern TX and then points north-northeast, possibley all the way into TN and KY.

Strong +40kt SW LLJ --> http://www.rap.ucar.edu/weather/model/disp...hr132hr144hr156

And the resultant moisture advection --> http://www.rap.ucar.edu/weather/model/disp...hr132hr144hr156

 

[Jim Bishop]

This has potential to be a significant severe weather event for East Texas/Louisiana & Arklatex on Sunday. Too early for any specifics. Let's just say I'm a little upset my flight from Nashville (for Thanskgiving) doesn't land in Houston 'till 4pm Sunday...

 

[Ronnie Bradley]

I've been watching GFS model maps regarding the upcoming setup since Sunday and last night, it shows a rather potent low w/ neutral trough moving ENE from SRn New Mexico to SE Kansas / NE Oklahoma by 0Z Monday. After the potent low and trough move out, another big trough will dig in the western third of the US and usher in some rather cold air.
The 500mb vort maps ( 0Z Monday) over at COD show the low as being rather potent.

Right now, the low is sitting west of California out in the ocean waiting to move east. It looks pretty good on visible and water vapor satellite.

Whether or not all this pans out remains to be seen. But it appears that the weather for next week looks to be unsettled for the US. Particularily the Northern 2/3rds (including the mid-south).

 

[Brett Adair]

Whoa buddy, do I like what I see. This is a setup that really favors significant severe over my area. The 18z model run has pushed the main upper level energy a bit further north and I don't really buy that. The SFC low also runs up towards IL from OK.....simply nuts with the pattern we are in. I don't see the trough wrapping up that fast.

I had my doubts about the atmosphere charging back up, but with the LLJ kicking above 60-65kts by 12z MON across western portions of the BMX CWA. All in all, it looks like a big outbreak across the Mid-south with damaging winds, large hail and possibly strong tornadoes in store.

Another chaser fest to come. :twisted:

 

[nickgrillo]

Well, the event is still nearly 102hrs out, but will make a more detailed forecast... After a review of the 12z GFS there sdoes appear to be potential for a widespread damaging wind event, along with the potential for a few tornadoes, especially with any discrete cells that form along the dryline. Based on the GFS forecast, low-level cyclogenesis will be underway during the start of the period, with a 40-50kt SW LLJ likely advecting in the progged surface Tds into the low 60s across the southern half of the warm sector. In general, the 80-125kt SW upper flow atop backed / nearly backed boundary layer flow south and east of the low creates a very favorable shear environment for fast-moving, strong supercells. The strong low-level wind fields and a favorabley saturated low-level airmass will help create a well-mixed boundary layer, particularly across eastern TX, into LA and AR and then possibley stretching into TN and MS during the late afternoon. Overall, this pretty much looks like a SLIGHTLY less significant version of last Tuesday, and from the looks of it now -- I would have to bet on widespread damaging winds and at least a few tornadoes (with a more concentrated threat area along the dryline across the southern half of the warm sector, with another threat area extending all the way into the OH valley, again, near the warm front).

 

[Carrie Halliday]

Nice to see that our second season is gearing up. Am watching and waiting to see if this manifests into one heck of a day for my area. I may give up my seat at Reliant and go 'nader hunting. :lol:

Will be watching and comaparing everyone's input, especially on Saturday.

 

[Dave Ewoldt]

Still a few days out...but the models have been fairly steady during the past few runs.... so with "some" confidence I offer....

If I had the day off...i would be tempted to make a run up i-35 and play the potential for a low-topped supercell event near the kansas turnpike northeast of wichita. Classic upper system/surface cyclone will produce very nice low and deep layer shear profiles....and the latest nam creates a bullseye of 3 km cape just east of the surface low as it wraps 55F sfc dews back into eastern kansas. I don't think a 'nader or two would be out of the question.

.....of course now, the 12z nam is quicker with the system pushing the threat more toward the mo/ks border....but also has the surface wave more stretched out nne/ssw with not as much turning in the lower levels.

 

[Jim Bishop]

This could be a repeat of Nov. 12, but this time over southern Iowa/Northern Missouri. The shear will be amazing, the cap will be strong, and there will be strong dynamics in place. 850mb moisture is going to be a problem, but it doesn't appear like surface moisture will be as much of a problem.

Like the Nov. 12th setup, this is very conditional on everything coming together just right. But once again this could be a significant severe weather event with tornadoes.

 

[Scott Weberpal]

Luckily I'm in St. Louis for the weekend visiting a friend. I don't think it'll hurt to chase on my way back to Wisconsin.

Latest NAM gives me decent confidence for Central and Northern parts of Missouri into S. IA. Surface moisture well juxtaposed with upper flow at very least leads me to believe dynamic forcing will be strong enough for some severe convecting. Obviously strong surface based convection is conditional based on moisture depth/diurnal heating. After chasing Nov. 12 and the horrendous day it was, I'm a little pessimistic about Sunday. However, being in St. Louis right now I make take my chances.

 

[Mikey Gribble]

I think tornadoes are a decent possibility on Sunday, but there are also some serious problems with this setup IMO. My biggest concerns right now are storm motion(40-50kts), terrain(poor road networks, hills, and trees), and cloud cover/instability(lapse rates aren't very steep according to the 0Z NAM). Great dynamics can't trump all of those problems, but it will definitely keep me watching. I'll just have to wait and see what it looks like tomorrow.

 

[nickgrillo]

After looking over the models, there is still some pretty good potential for this system. A strengthening SW LLJ will allow for rapid deep moisture transport toward the Mississippi valley beginning tomorrow, and continue through the day on Sunday. Surface cyclogenesis will be underway during the start of the period, with the surface low near the TX/OK panhandles forecasted to deepen as it pushes eastward toward the Mississippi valley by Sunday morning. Relatively moist and backed boundary layer flow beneath SW 60-80kt mid-level flow yields favorable deep-layer vertical shear profiles for supercell structures, with NAM bringing in 200-400m2/s2 0-1km SRH across the warm sector, given the backed surface flow pattern, which will increase the potential for tornadoes with any surface-based storms. I think the area east of the dryline will see adequate convergance by early afternoon to initiate deep convection, and any sustained surface-based storm should be able to take on a supercellular structure, given strongly sheared and at least marginally buoyant boundary layer airmass -- I would have to agree with Scott's target area of central MO, which is where I would play.

 

[Brett Adair]

Michael has a good point on storm motion in this situation. Good luck catching these things with the increasing wind profiles. I also think Nick is onto something ahead of the dryline and further east along the warm frontal boundary. Given the steepe height falls progged and strengthening SFC low, the gradient that forms along the squall line will also favor tornadoes considering it will allow small scale backing at the SFC given the gradient just ahead of the line.

 

[afischer]

Well the 12z NAM is definitely an improvement over the 00Z NAM, having flopped back to a far less progressive/less strung out solution. Not sure if the GFS has improved since 00z as I didn't see it, but the 12Z GFS looks similar to the 12z NAM. NAM/NAM-KF model soundings northeast of Kansas City remind me strongly of the Nov 12 event, with the models forecasting a significant 850-750mb cap to break explosively around 21Z as strong upper difluence and pva start to affect the area. If insolation isn't as strong or moisture is more shallow than the models suggest, than cap breakage may take longer as other posters have mentioned. Also agree w/ the storm speed being aproblem, particularly on the not-nice roads of northern MO. Degree of insolation and the ultimate convective mode look to be the big question marks to me right now.

 

[nickgrillo]

Well, things still look on track to me with the latest 12 runs... Strong forcing and backed boundary layer flow ahead of amplified mid-level impulse will weaken the inversion by mid-afternoon. Deep shear profiles favors a few isolated supercells forming ahead of the dryline by mid-afternoon, with the approach of shortwave around 21z, with marginal surface-based instability and strong deep/low-level shear favoring the potential for tornadoes. The storms should consolidate into a squall line with embedded supercell structures over eastern MO by the late evening, with a continued threat for tornadoes and damaging winds. Very favorable low-level wind fields has poised forecasted 200-400m2/s2 0-1km SRH across MO / IL by mid-day tomorrow. At this time, I would have to say damaging winds and at least a few tornadoes remain a decent threat for MO / IL through the afternoon and evening.

 

[nickgrillo]

After looking at more forecast soundings further to the west, it makes me think of northwest MO as a good target area. Unmodified EAX sounding at 21z SUN shows a well-mixed boundary layer, with dry adiabatic lapse rates present through the sfc-1.5km layer and strong veering flow. Steep low-level lapse rates and moist surface inflow yields 1391j/kg of sbCAPE, per this NAM forecast sounding, with no inversion left by 21z.